This invention relates to the recording of program material, such as music, voice and the like, and particularly to the recording of materials which are susceptible to unauthorized duplication or copying using the medium of magnetic tape.
Unauthorized copying or duplication of program material sold by publishers or their licensees is widespread in spite of its illegality and is difficult to police effectively. The result of such copying is to cut seriously into publishers' revenues and to discourage production of expensive, high quality programs. Such unauthorized copying takes place for the most part through the use of tape cassettes as the medium for generating the unauthorized copies. Other forms of tape are sometimes used, but the tape medium in general, and tape cassettes in particular, account for most of this activity.
Accordingly, it is desirable to develop techniques and equipment for preparing the original recordings of the program material to discourage or prevent the making of unauthorized copies, or at least to leave traces or "fingerprints" on the copies which will supply irrefutable proof of the origin of the program material and the fact that unauthorized copies have been made.
Any technique for preparing original program material so as to prevent or render detectable its duplication upon tape should satisfy several criteria. The technique should be simple and economical to use. In addition, the technique should not interfere with normal playback of the material by the possessor of an authorized recording. Moreover, the technique should be one that is difficult for a tape pirate to nullify or sidestep. Finally, the technique preferably should spoil the unauthorized copies so that they are unsatisfactory and unsaleable, or at least should permit ready identification of a tape recording as an unauthorized copy.
Heretofore, no techniques have been developed which satisfy the foregoing criteria.